Recently, various LCD products have become popular for use in mobile hand-held devices. In addition, due to widespread use of smart end devices, integration of a touch function into smart end devices has become a mainstream demand for current products.
A frame period of a conventional mobile apparatus includes a display scanning period and a touch sensing period, such that scan signals G(1)-G(N) are outputted during the display scanning period to drive scan lines of a display panel, and then sensing signals S(1)-S(N) are outputted during the touch sensing period to drive sensing lines of a touch panel. The display scanning period may include a plurality of enable periods of scan lines, and a time interval between neighboring enable periods of the scan lines is a display stop period, during which display scanning is suspended to perform touch sensing, and thus no scan signals is outputted to the mobile apparatus. FIG. 1 is a schematic circuit diagram of a shift register circuit 100 in a single-phase shift register. An nth-stage shift register circuit 100 has a driving unit 110, a pull-up unit 120, a pull-down unit 130, and a pull-down control unit 140, wherein the pull-up unit 120 is conducted according to the previous-stage scan signal (e.g., the scan signal G(n−1)) to raise the voltage at a driving node Q to a high voltage level, and the driving unit 110 is conducted according to clock signals CK1/XCK1 to output the scan signal G(n).
FIG. 2 is a schematic waveform diagram of internal nodes and scan signals of the shift register circuit 100. During one frame period, after the scan signal G(n) is outputted, a display stop period begins. During the display stop period, the signals provided by a timing controller 300, such as the clock signals CK1/XCK1, are disabled to suspend outputting a scan signal G(n+1). Since the clock signals CK1/XCK1 are disabled, the driving units 110 of the nth-stage and the (n+1)th-stage shift register circuits 100 are in a cut-off state. However, the pull-up units 120 of the nth-stage and the (n+1)th-stage shift register circuits 100 has received the previous-stage scan signals, such that the voltages of the driving nodes Q of the nth-stage and the (n+1)th-stage shift register circuits 100 are maintained at a high voltage level, and thus causing transistors of the driving units 110 to be stressed due to bias voltages continuously acting on the driving units 110. Long time stressing reduces the reliability of the driving units 110, such that the scan signal G(n) is not outputted at a desired voltage level, thereby degrading display quality.
Thus, how to prevent the driving transistor of the shift register circuits from being stressed for a long time, resulting in component performance deterioration and thus erroneous output is one of the important development issues today, and also has become an object urgently in need of improvement in related fields today.